After counting down the Top 5 WTA tournament matches of 2018, our year-end review moves to the biggest upsets of the season. First up is Zhang Shuai's stunning victory over Sloane Stephens at the first Grand Slam of the year at the Australian Open.
WHAT HAPPENED: The first Grand Slam fortnight of the year had hardly begun, but Zhang Shuai served up a statement result on the first day of play at the 2018 Australian Open.
The unseeded World No.34 rallied from a set and a break down - breaking serve to stay in the match in the second set - to defeat then-reigning US Open champion Sloane Stephens in a wild three-setter on Margaret Court Arena, 2-6, 7-6(2), 6-2.
Read the match report: Zhang denies Stephens in Melbourne upset
The American was the first seed to fall at this year's edition of the Australian Open, as she was unable to hold off a tenacious effort from Zhang despite serving for the match.
Stephens began the match in total command, hitting 14 winners and making just nine unforced errors compared to Zhang’s five winners and 15 errors in the opener, but the latter began to work the court over the course of the match.
Stephens rallied from a break down in the second set to serve for a spot in the second round at 6-2, 5-4, but ultimately fell to the then-Chinese No.1 for the second time in four career meetings.
The stunning victory was the latest in a string of career moments for Zhang at the Australian Open: after going 0-14 in Grand Slam matches to begin her career, the Chinesewoman made a career-defining run to the last eight as a qualifier in 2016, having contemplated retiring from the sport completely before that.
Her run that year included a first-round victory over then-World No.2 Simona Halep on that very same Margaret Court Arena.
WHAT THEY SAID: The former quarterfinalist captured some of the same magic on the second show court in Melbourne, and told all assembled there that the good feelings from her breakout result two years ago had not yet left.
"[Margaret Court Arena] is really special for me,” Zhang said in her on-court interview. “When I came back here to warm up, I was feeling so excited.
"So I think I was ready today...I always play against great players on this court. I was very happy to play against Sloane. When she was serving for the match, I was a little bit sad because I didn’t want to go home, so I kept telling myself to try my best in every game."
After her career-defining triumph in Flushing Meadows, the season-opening defeat for Stephens in her first Grand Slam match as a major champion was her eighth consecutive loss - a late-2017 swoon which continued into the early stages of 2018.
"It's not tough times. It's just a learning experience. It's a long journey," the American said after the match. "This year, it's a new year, only the second tournament of the year. It's a long road and long season ahead.
"Tennis is definitely a roller coaster. But I have learned to just not panic. It will be okay. There's always going to be times when it's really tough and there will be times when you're on an extreme high. I think for me now it's not that great, but it's nothing to panic about."
WHAT IT MEANT: As she said she would, Stephens ended up beating a fair few 'someones' in 2018 - as she compiled a 37-19 record on the season, won the Miami Open, reached her second Grand Slam final at the French Open and qualified for the BNP Paribas Finals Singapore presented by SC Global for the first time.
She snapped her losing streak at her next event after Melbourne, as she reached the quarterfinals in Acapulco - and went on to reach the quarterfinals or better at six events overall.
With five Top 5 wins to her name in 2018, Stephens was tied for the tour lead in that category, alongside Kiki Bertens and Daria Kasatkina, and reached a career-best ranking of World No.3 in the summer.